Golf ball core compositions

ABSTRACT

The present invention is directed to improved polybutadiene compositions suitable for use in molded golf ball core construction. The improved polybutadiene compositions are composed of polypropylene powder resins which have the effect of increasing the hardness of the resulting molded cores without increasing the weight upon curing, thereby allowing for a reduction in the amount of crosslinking agents utilized and increasing the amount of fillers incorporated therein. The addition of the polypropylene powder resins to the core compositions lowers the cost of the molded core, while maintaining the proper weight and compression. The present invention is also directed to golf balls produced utilizing the improved core compositions. Furthermore, the invention is directed to a method for reducing the amount of crosslinking agents utilized to formulate a core composition through the incorporation of polypropylene powder resins. In addition, a method for decreasing the amount of crosslinking agents and increasing the amount of mineral fillers included in a core composition through the incorporation of polypropylene powder resins is also disclosed.

This is a continuation of U.S. application Ser. No. 08/819,945, filedMar. 18, 1997 now U.S. Pat. No. 5,895,105; which is a continuation ofU.S. application Ser. No. 08/370,224, filed Jan. 9, 1995 (abandoned);which is a continuation of U.S. application Ser. No. 08/893,277, filedJun. 4, 1992 (abandoned), which is a continuation-in-part of U.S.application Ser. No. 07/874,066, filed on Apr. 24, 1992 (abandoned).

BACKGROUND OF THE INVENTION

The present invention is directed to improved polybutadiene compositionsfor use in molded golf ball core construction. The improvedpolybutadiene compositions contain polypropylene powder resins, whichhave the effect of increasing the hardness of the resulting molded coreswithout increasing the weight and/or substantially reducing theresiliency of the ball. The present invention is also directed to golfballs produced utilizing the improved core compositions.

Moreover, it has been found that the addition of the particulatepolypropylene allows for a reduction in the amount of crosslinkingagents utilized in the core compositions and/or an increase in theamount of higher specific gravity fillers, thereby dramaticallydecreasing the cost of the golf ball cores. A method for producing suchan effect is also disclosed.

Two of the principal properties involved in the performance of golfballs are resilience and hardness. Resilience is determined by thecoefficient of restitution (C.O.R.), the constant “e”, which is theratio of the relative velocity of two elastic spheres after directimpact to that before impact, or more generally, the ratio of theoutgoing velocity to incoming velocity of a rebounding ball. As aresult, the coefficient of restitution (i.e. “e”) can vary from zero toone, with one being equivalent to an elastic collision and zero beingequivalent to an inelastic collision. Hardness is determined as thedeformation (i.e. compression) of the ball under various load conditionsapplied across the ball's diameter (i.e. the lower the compressionvalue, the harder the material).

Resilience (C.O.R.), along with additional factors such as clubheadspeed, angle of trajectory, and ball configuration (i.e. dimplepattern), generally determines the distance a ball will travel when hit.Since clubhead speed and the angle of trajectory are not factors easilycontrollable, particularly by golf ball manufacturers, the factors ofconcern among manufacturers are the coefficient of restitution (C.O.R.)and the surface configuration of the ball.

In this regard, the coefficient of restitution of a golf ball isgenerally measured by propelling a ball at a given speed against a hardsurface and measuring the ball's incoming and outgoing velocityelectronically. The coefficient of restitution must be carefullycontrolled in all commercial golf balls in order for the ball to bewithin the specifications regulated by the United States GolfersAssociation (U.S.G.A.). Along this line, the U.S.G.A. standards indicatethat a “regulation” ball cannot have an initial velocity (i.e. the speedoff the club) exceeding 255 feet per second (250 feet per second with a2% tolerance). Since the coefficient of restitution of a ball is relatedto the ball's initial velocity (i.e. as the C.O.R. of a ball isincreased, the ball's initial velocity will also increase), it is highlydesirable to produce a ball having a sufficiently high coefficient ofrestitution to closely approach the U.S.G.A. limit on initial velocity,while having an ample degree of hardness (i.e. impact resistance) toproduce enhanced durability.

The coefficient of restitution (C.O.R.) in solid core balls is afunction of the composition of the molded core and of the cover. Inballs containing a wound core (i.e. balls comprising a liquid or solidcenter, elastic windings, and a cover), the coefficient of restitutionis a function of not only the composition of the center and cover, butalso the composition and tension of the elastomeric windings.

The present invention relates to the addition of a polypropylene powderresin to polybutadiene core compositions, such as those disclosed inU.S. Pat. Nos. 4,726,590; 4,838,556; 4,844,471; and 4,852,884 in orderto produce solid golf ball cores and/or centers exhibiting enhancedhardness without an increase in weight and a, substantial reduction inC.O.R. It has been found that the addition of a polypropylene powderresin results in a core which is too hard (i.e. exhibits lowcompression) and thus allows for a reduction in the amount ofcrosslinking agent utilized to soften the core to a normal compression.

Furthermore, because polypropylene powder resin can be added to corecomposition without an increase in weight of the molded core uponcuring, the addition of the polypropylene powder allows for the additionof large amounts of higher specific gravity fillers, such as mineralfillers. Since the crosslinking agents utilized in the polybutadienecore compositions are expensive and/or the higher specific gravityfillers are relatively inexpensive, the addition of the polypropylenepowder resin substantially lowers the cost of the golf ball cores whilemaintain proper weight and compression.

Along these lines, although other particulate thermoplastic materialshave been evaluated, including relatively low specific gravitythermoplastic powders (i.e. polystyrene, polyethylene, polymethylmethacrylate, etc.), it has been found that these powdered resins do notincrease the hardness of the cores to the degree desired, thus stillrequiring use of larger amounts of the expensive crosslinking agentssuch as zinc diacrylate, and/or they reduce the C.O.R. values toundesirable ranges. Furthermore, the alternative thermoplastic powderresins produce, when compounded, heavier cores than the presentinvention. Consequently, the addition of the inexpensive mineral fillersis substantially limited in the powdered plastics in comparison .to thepresent invention.

Accordingly, it is an object of the present invention to provideimproved polybutadiene core compositions which, when utilized toformulate golf balls., produce golf balls exhibiting enhanced hardnessat a lower weight due to the composition of the core. An additionalobject of the invention is to provide cores or centers for theconstruction of solid or wound golf balls which dramatically lower thecost of the golf ball while maintaining proper weight and compression.Furthermore, since a golf ball produced in accordance with the presentinvention exhibits an enhanced hardness at a lower weight, it ispossible to increase the durability of the ball by adding additionaldurability enhancers without greatly sacrificing the ball's overallweight and/or composition. A still further object of the invention is toproduce golf ball cores or centers which maintain their roundness andshape upon continued impact by a golf club.

These and other objects and features of the invention will be apparentfrom the following summary and description of the invention and from theclaims.

SUMMARY OF THE INVENTION

In one aspect, the present invention is directed to an improvedcomposition for golf ball core production comprising a base elastomerselected from polybutadiene and mixtures of polybutadiene with otherelastomers, at least one metallic salt of an unsaturated carboxylic acid(a co-crosslinking agent), a free radical initiator (a co-crosslinkingagent) and a polypropylene powder resin. In addition, suitable andcompatible modifying ingredients including, but not limited to, metaloxide activators, fatty acids, fillers and other additives may beincluded. In an additional aspect, the present invention relaters to agolf ball comprising a solid core and a cover therefor, the solid coreconsisting of a base elastomer selected from polybutadiene and mixturesof polybutadiene with other elastomers, at least one metallic salt of anunsaturated carboxylic acid, a free radical initiator and a particulatepolypropylene powder, and the cover comprising one or more layers ofionomer resin-based compositions.

In a further aspect, the present invention is directed to a method forreducing the amount of crosslinking agent utilized to formulate a corecomposition through the incorporation of a polypropylene powder resin.In a still further aspect, a method for decreasing the amount of acrosslinking agent and increasing the amount of mineral fillers in acore composition through the incorporation of a polypropylene powderresin is also disclosed.

Further scope of the applicability of the invention will become apparentfrom the detailed description provided below.

DETAILED DESCRIPTION OF THE INVENTION

The present invention is directed to improved core compositions which,when utilized for golf ball core construction, produce cores exhibitingenhanced hardness without an increase in weight and/or a decrease inresilience. In this regard, it has been found that the addition of apolypropylene powder resin to polybutadiene core compositions has theeffect of increasing the hardness of the resultant cores.

In addition, the present invention is directed to the discovery that theparticulate polypropylene powder can be added to various polybutadienecore compositions as a cost: effective means of lowering compression(i.e. hardness) or the molded cores. Since the addition of thepolypropylene powder produces cores that are too hard, a substantialreduction in the use of expensive crosslinking agents, such as zincdiacrylate, can be achieved in order to soften the center to a normalcompression.

Furthermore, because the specific gravity of polypropylene is very low(0.90 g/cm³) and the polypropylene powders produce a lighter weightmolded core upon curing, large amounts of higher specific gravity, lessexpensive, mineral fillers such as calcium carbonate can be utilized. Asa result, the addition of the particulate polypropylene powderdramatically lowers the cost of the core composition while maintainingthe weight and compression desired.

The polypropylene (C₃H₅) powder suitable for use in the presentinvention has a specific gravity of about 0.90 g/cm³, a melt flow rateof about 4 to about 12 and a particle size distribution of greater than99% through a 20 mesh screen. Examples of such polypropylene powderresins include those sold by the Amoco Chemical Co., Chicago, Ill.,under the designations “6400 P”, “7000 P” and “7200 P”. The typicalproperties of these resins are listed below:

Properties of Resin 6400 P 7000 P 7200 P Melt flow rate, ASTM D1238,2.16 kg at 4 10 12 230° C. Density, ASTM D792 at 23° C. g/cm³ 0.90 0.900.90 Particle size distribution, ASTM D1921 0 0 0 12 screen mesh, %retained >99 >99 >99 smaller than 140 screen mesh, % <1 <1 <1

In general, polypropylene (unfilled) possess the following properties:

ASTM Poly- test propylene Properties method Unfilled 1. Meltingtemperature, ° C. 160-175 T_(m) (crystalline) 2. Processing temperaturerange, ° F. I: 400-550 (C = compression; T = transfer; E: 400-500 I =Injection; E = extrusion) 3. Molding pressure range, 10³ p.s.i. 10-20 4.Compression ratio 2.0-2.4 5. Mold (linear) shrinkage, in./in. D9550.010-0.025 6. Tensile strength at break, p.s.i. D638 4500-6000 7.Elongation at break, % D638 100-600 8. Tensile yield strength, p.s.i.D638 4500-5400 9. Compressive strength (rupture or yield), D6955500-8000 p.s.i. 10. Flexural strength (rupture or yield), p.s.i. D7906000-8000 11. Tensile modulus, 10³ p.s.i. D638 165-225 12. Compressivemodulus, 10³ p.s.i. D695 150-300 13. Flexural modulus, 10³ p.s.i 73° F.D790 170-250 200° F. D790 50 250° F. D790 35 300° F. D790 14. Izodimpact, ft.-lb./in. of notch D256A 0.4-1.2 (¼-in. thick specimen) 15.Hardness Rockwell D785 R80-102 Shore/Barcol D2240/ 25833 16. Coef. oflinear thermal expansion, D696 81-100 10⁻⁸ in./in.° C. 17. Deflectiontemperature 264 p.s.i. D648 120-140 under flexural load, ° F. 66 p.s.i.D648 225-250 18. Thermal conductivity, 10⁻⁴ cal.-cm./ C177 2.8sec.-cm.²° C. 19. Specific gravity D792 0.900-0.910 20. Water absorption(⅛-in. 24 hr. D570 0.01-0.03 thick specimen), % Saturation D570 21.Dielectric strength (⅛-in. D149 600 thick specimen), short time, v./mil

It has been found that the addition of polypropylene in particulateform, such as polypropylene powder resins, substantially enhances thedesired properties of the core compositions over known golf ball coreadditives including other known thermoplastic polymers in powdered form.

The core compositions and resulting molded golf balls of the presentinvention containing the particulate polypropylene resins aremanufactured using conventional ingredients and techniques. In thisregard, the core compositions of the invention may be based onpolybutadiene, and mixtures of polybutadiene with other elastomers. Itis preferred that the base elastomer have a relatively high molecularweight. The broad range for the molecular weight of suitable baseelastomers is from about 50,000 to about 500,000. A more preferred rangefor the molecular weight of the base elastomer is from about. 100,000 toabout 500,000. As a base elastomer for the core; composition,cis-polybutadiene is preferably employed, or a blend ofcis-polybutadiene with other elastomers may also be utilized. Mostpreferably, cis-polybutadiene having a weight-average molecular weightof from about 100,000 to about 500,000 is employed. Along this line, ithas been found that the high cis-polybutadiene manufactured and sold byShell Chemical Co., Houston, Tex., under the tradename Cariflex BR-1220,and the polyisoprene available from Muehlstein, H & Co., Greenwich,Conn. under the designation “SKI 35” are particularly well suited.

The unsaturated carboxylic acid component of the core composition (aco-crosslinking agent) is the reaction product of the selectedcarboxylic acid or acids and an oxide or carbonate of a metal such aszinc, magnesium, barium, calcium, lithium, sodium, potassium, cadmium,lead, tin, and the like. Preferably, the oxides of polyvalent metalssuch as zinc, magnesium and cadmium are used, and most preferably, theoxide is zinc oxide.

Exemplary of the unsaturated carboxylic acids which find utility in thepresent core compositions are acrylic acid, methacrylic acid, itaconicacid, crotonic acid, sorbic acid, and the like, and mixtures thereof.,Preferably, the acid component is either acrylic or methacrylic acid.Usually, from about 20 to about 50, and preferably from about 2.5 toabout 35 parts by weight of the carboxylic acid salt, such as zincdiacrylate, is included in the core composition. The unsaturatedcarboxylic acids and metal salts thereof are generally soluble in theelastomeric base, or are readily dispersible.

The free radical initiator included in the cores composition is anyknown polymerization initiator (.a co-crosslinking agent) whichdecomposes during the cure cycle. The term “free radical initiator” asused herein refers to a chemical which, when added to a mixture of theelastomeric blend and a metal salt of an unsaturated, carboxylic acid,promotes crosslinking of the elastomers by the metal salt of theunsaturated carboxylic acid. The amount of the selected initiatorpresent is dictated only by the requirements of catalytic activity as apolymerization initiator. Suitable initiators include peroxides,persulfates, azo compounds and hydrazides. Peroxides which are readilycommercially available are conveniently used in the present invention,generally in amounts of from about 0.1 to about 10.0 and preferably inamounts of from about 0.3 to about 3.0 parts by weight per each 100parts of elastomer.

Exemplary of suitable peroxides for the purposes of the presentinvention are dicumyl peroxide, n-butyl 4,4′-bis (butylperoxy) valerate,1,1-bise(t-butylperoxy)-3,3,5-trimethyl cyclohexane, di-t-butyl peroxideand 2,5-di-(t-butylperoxy)-2,5 dimethyl hexane and the like, as well asmixtures thereof. It will be understood that the total amount ofinitiators used will vary depending on the specific end product desiredand the particular initiators employed.

Examples of such commercial available peroxides are Luperco 230 or 231XL, a peroxyketal manufactured and sold by Atochem, Lucidol Division,Buffalo, N.Y., and Trigonox 17/40 or 29/40, al,1-di-(t-butylperoxy)-3,3,5-trimethyl cyclohexane sold by Akzo ChemieAmerica, Chicago, Ill. The one hour half life of Luperco 231. XL isabout 112° C., and the one hour half life of Trigonox 29/40 is about129° C.

The core compositions of the present invention may additionally containany other suitable and compatible modifying ingredients including, butnot limited to, metal oxides, fatty acids, and diisocyanates. Forexample, Papi 94, a polymeric diisocyanate, commonly available from DowChemical Co., Midland, Mich., is an optional component in the rubbercompositions. It can range from about 0 to 5 parts by weight per 100parts by weight rubber (phr) component, and acts as a moisturescavenger.

Various activators may also be included in the compositions of thepresent invention. For example, zinc oxide and/or magnesium oxide areactivators for the polybutadiene. The activator can range from about 2to about 30 parts by weight per 100 parts by weight of the rubbers (phr)component.

Moreover, filler-reinforcement agents may be added to the composition ofthe present invention. Since the specific gravity of polypropylenepowder is very low, and when compounded, the polypropylene powderproduces a lighter molded core, large amounts of higher gravity fillersmay be added. Additional benefits may be obtained by the incorporationof relatively large amounts of higher specific gravity, inexpensivemineral fillers such as calcium carbonate. Such fillers as areincorporated into the core compositions should be in finely dividedform, as for example, in a size generally less than about 30 mesh andpreferably less than about 100 mesh U.S. standard size. The amount ofadditional filler included in the core composition is primarily dictatedby weight restrictions and preferably is included in amounts of fromabout 10 to about 1.00 parts by weight per 100 parts rubber.

The preferred fillers are relatively inexpensive and heavy and serve tolower the cost of the ball and to increase the weight of the ball toclosely approach the U.S.G.A. weight limit of 1.620 ounces. Exemplaryfillers include mineral fillers such as limestone, silica, mica barytes,calcium carbonate, or clays. Limestone is ground calcium/magnesiumcarbonate and is used because it is an inexpensive, heavy filler.

As indicated, ground flash filler may be incorporated and is preferably20 mesh ground up center stock from the excess flash from compressionmolding. It lowers the cost and may increase the hardness of the ball.

Fatty acids or metallic salts of fatty acids may also be included in thecompositions, functioning to improve moldability and processing.Generally, free fatty acids having from about 10 to about 40 carbonatoms, and preferably having from about 15 to about 20 carbon atoms, areused. Exemplary of suitable fatty acids are stearic acid and linoleicacids, as well as mixtures thereof. Exemplary of suitable metallic saltsof fatty acids include zinc stearate. When included in the corecompositions, the fatty acid component is present in amounts of fromabout 1 to about 25, preferably in amounts from about 2 to about 15parts by weight based on 100 parts rubber (elastomer).

It is preferred that the core compositions include stearic acid as thefatty acid adjunct in an amount of from about 2 to about 5 parts byweight per 100 parts of rubber.

Diisocyanates may also be optionally included in the core compositionswhen utilized, the diioscyanates are included in amounts of from about0.2 to about 5.0 parts by weight based on 100 parts rubber. Exemplary ofsuitable diisocyanates is 4,4′-diphenylmethane diisocyanate and otherpolyfunctional isocyanates know to the art.

Furthermore, the dialkyl tin difatty acids set forth in U.S. Pat. No.4,844,471, the dispersing agents disclosed in U.S. Pat. No. 4,838,556,and the dithiocarbonates set forth in U.S. Pat. No. 4,852,884 may alsobe incorporated into the polybutadiene compositions of the presentinvention. The specific types and amounts of such additives are setforth in the above identified patents, which are incorporated herein byreference.

The golf ball core compositions of the invention are generally comprisedof the addition of about 1 to about 100 parts by weight of particulatepolypropylene resin (preferably about 10 to about 100 parts by weightpolypropylene powder resin) to core compositions comprised of 100 partsby weight of a base elastomer (or rubber) selected from polybutadieneand mixtures of polybutadienes with other elastomers, 20 to 50 parts byweight of at least one metallic salt of an unsaturated carboxylic acid,and l to 10 parts by weight of a free radical initiator. Morepreferably, the particulate polypropylene resin utilized in the presentinvention comprises from about 20 to about 40 parts by weight of apolypropylene powder resin such as that trademarked and sold by AmocoChemical Co. under the designation “6400 P”, “7000 P” and “7200 P”. Theratios of the ingredients may vary and are best optimized empirically.

As indicated above, additional suitable and compatible modifying agentssuch as fatty acids, and secondary additives such as Pecan shell flour,ground flash (i.e. grindings from previously manufactured cores ofsubstantially identical construction), barium sulfate, zinc oxide, etc.may be added to the core compositions to increase the weight of the ballas necessary in order to have the ball reach or closely approach theU.S.G.A. weight limit of 1.620 ounces.

In producing golf ball cores utilizing the present compositions, theingredients may be intimately mixed using, for example, two roll millsor a Banbury mixer until the composition is uniform, usually over aperiod of from about 5 to about 20 minutes. The sequence of addition ofcomponents is not critical. A preferred blending sequence is as follows.

The elastomer, polypropylene powder resin, fillers, zinc salt, metaloxide, fatty acid, and the metallic dithiocarbamate (if desired),surfactant (if desired), and tin difatty acid (if desired), are blendedfor about 7 minutes in an internal mixer such as a Banbury mixer. As aresult of shear during mixing, the temperature rises to about 200° F.The initiator and diisocyanate are then added and the mixing continueduntil the temperature reaches about 220° F. whereupon the batch isdischarged onto a two roll mill, mixed for about one minute and sheetedout.

The sheet is then placed in a Barwell preformer and slugs are produced.The slugs are then subjected to compression molding at about 320° F. forabout 14 minutes. After molding and cooling, the cooling effected atroom temperature for about 4 hours, the molded cores are subjected to acenterless grinding operation whereby a thin layer of the molded core isremoved to produce a round core having a diameter of 1.545 inches.

The mixing is desirably conducted in such a manner that the compositiondoes not reach incipient polymerization temperatures during the blendingof the various components.

Usually the curable component of the composition will be cured byheating the composition at elevated temperatures on the order of fromabout 275° F. to about 350° F., preferably and usually from about 290°F. to about 325° F., with molding of the composition effectedsimultaneously with the curing thereof. The composition can be formedinto a core structure by any one of a variety of molding techniques,e.g. injection, compression, or transfer molding. When the compositionis cured by heating, the time required for heating will normally beshort, generally from about 10 to about 20 minutes, depending upon theparticular curing agent used. Those of ordinary skill in the artrelating to free radical curing agents for polymers are conversant withadjustments of cure times and temperatures required to effect optimumresults with any specific free radical agent.

After molding, the core is removed from the mold and the surfacethereof, preferably treated to facilitate adhesion thereof to thecovering materials. Surface treatment can be effected by any of theseveral techniques; known in the art, such as corona discharge, ozonetreatment, sand blasting, and the like. Preferably, surface treatment iseffected by grinding with an abrasive wheel.

The core is converted into a golf ball by providing at: least one layerof covering material thereon, ranging in thickness from about 0.050 toabout 0.250 inch and preferably from about 0.060 to about 0.090 inch.The cover composition preferably is made from ethylene-acrylic acid orethylene-methacrylic acid copolymers neutralized with mono or polyvalentmetals such as sodium, potassium,, lithium, calcium, zinc, or magnesium.

The ionic copolymers used to produce the cover compositions may be madeaccording to known procedures, such as those in U.S. Pat. No. 3,421,766or British Patent No. 963,380, with neutralization effected according toprocedures disclosed in Canadian Patent No. 674,595 and 713,631, whereinthe ionomer is produced by copolymerizing the olefin and carboxylic acidto produce a copolymer having the acid units randomly distributed alongthe polymer chain. The ionic copolymer comprises one or more α-olefinsand from about 9 to about 15 weight percent of α, β-ethylenicallyunsaturated mono- or dicarboxylic acid, the basic copolymer neutralizedwith metal ions to the extent desired.

At least 18% of the carboxylic acid groups of the copolymer areneutralized by the metal ions, such as sodium, potassium, zinc, calcium,magnesium, and the like, and exist in the ionic state.

Suitable olefins for use in preparing the ionomeric resins include,. butare not limited to,, ethylene, propylene, butene-1, hexene-1, and thelike. Unsaturated carboxylic acids include, but are not limited to,acrylic, methacrylic, ethacrylic, α-chloroacrylic, crotonic, maleic,fumaric, itaconic acids, and the like. Preferably, the ionomeric resinis a copolymer of ethylene with acrylic and/or methacrylic acid, such asthose disclosed in U.S., Pat. Nos. 4,884,814; 4,911,451; 4,986,545 and5,098,105, incorporated herein by reference.

In this regard, the ionomeric resins sold by E. I. DuPont de NemoursCompany under the trademark “Surlyn®”, and the ionomer resins sold byExxon Corporation under either the trademark “Escort®” or the tradename“Iotek” are examples of commercially available ionomeric resins whichmay be utilized in the present invention. The ionomeric resins soldformerly under the designation “Escor®” and now under the new name“Iotek”, are very similar to those sold under the “Surlyn®” trademark inthat the “Iotek” ionomeric resins are available as sodium of zinc saltsof poly(ethylene acrylic acid) and the “Surlyn” resins are available aszinc or sodium salts of poly(ethylene methacrylic acid). In additionvarious blends of “Iotek” and “Surlyn®” ionomeric resins, as well asother available ionomeric resins, may be utilized in the presentinvention.

In the embodiments of the invention that are set forth below in theExamples, the cover included acrylic acid ionomer resin having thefollowing compositions:

% weight Iotek 4000 (7030)¹ 52.4 Iotek 8000 (900)² 45.3 Unitane 0-110³2.25 Ultramarine blue⁴ 0.0133 Santonox R⁵ 0.0033 ¹Iotek 4000 is a zincsalt of poly (ethylene acrylic acid) ²Iotek 8000 is a sodium salt ofpoly (ethylene acrylic acid) ³Unitane 0-100 is a titanium dioxide soldby Kemira Inc., Savannah, GA. ⁴Ultramarine Blue is a dye sold byWhitaker, Clark, and Daniels of South Painsfield, N.J. ⁵Santonox R is aantioxidant sold by Monsanto, St. Louis, MO.

The covered golf ball can be formed in any one of the several methodsknown to the art. For example, the molded core may be placed in thecenter of a golf ball mold and the ionomeric resin-containing covercomposition injected into and retained in the space for a period of timeat a mold temperature of from about 40° F. to about 120° F.

Alternatively, the cover composition may be injection molded at about300° F., to about 450° F. into smooth-surfaced hemispherical shells, acore and two such shells placed in a dimpled golf ball mold and unifiedat temperatures on the order of from about 100° F. to about 200° F.

The golf ball produced is then painted and marked, painting beingeffected by spraying techniques.

The present invention is further illustrated by the following examplesin which the parts of the specific ingredients are by weight. It is tobe understood that the present invention is not limited to the examples,and various changes and modifications may be made in the inventionwithout departing from the spirit and scope thereof.

EXAMPLE 1

Using the ingredients tabled below, golf ball cores having a finisheddiameter of about 1.540 to about 1.545 inches were produced bycompression molding and subsequent removal of a surface layer bygrinding. Each core was formulated using 100 parts elastomer (rubber).In the formulations, the amounts of remaining ingredients are expressedin parts by weight, and the degrees of coefficient of restitution andcompression achieved are set forth below. The data for these examplesare the averages for twelve cores which were produced for each example.The properties of the molded cores produced from each formulation weremeasured according to the following parameters:

Riehle compression is a measurement of the deformation of a golf ball ininches under a fixed static load of 200 pounds.

Coefficient of restitution (C.O.R.) was measured by firing the resultinggolf ball in an air cannon at a velocity of 125 feet per second againsta steel plate which is positioned 12 feet from the muzzle of the cannon.The rebound velocity was then measured. The rebound velocity was dividedby the forward velocity to give the coefficient of restitution.

TABLE 1 Effect of the Addition of Polypropylene Powder Resin on theProperties of the Molded Core Formulations Ingredients 1 2 3 4 5 6 7 8BR-1220¹ 90 90 90 90 90 90 90 90 SKI-35² 10 10 10 10 10 10 10 10 ZDA³ 3131 31 31 27 23 23 23 ZnO 6.0 6.0 6.0 6.0 6.0 6.0 6.0 6.0 Zinc Stearate15 15 15 15 15 15 15 15 Limestone 18 18 18 18 18 18 28 38 Grd Flash 2020 20 20 20 20 20 20 6400 P⁴ 0 20 30 40 30 30 30 30 Trig 17/40⁵ 1.5 1.51.5 1.5 1.5 1.5 1.5 1.5 Papi 94⁶ .5 .5 .5 .5 .5 .5 .5 .5 Total 192.0212.0 222.0 232.0 218.0 214.0 224.0 234.0 Properties Molded Core Size,inches 1.539 1.539 1.538 1.539 1.540 1.540 1.540 1.540 Wgt., grams 36.535.6 35.1 34.8 35.0 34.6 35.6 36.7 Comp. (Riehle) .064 .057 .056 .054.060 .065 .065 .062 {overscore (e)} (C.O.R.) .796 .783 .773 .763 .767.760 .752 .747 Molded Ball Size, inches 1.683 1.683 1.682 1.683 1.6831.683 1.683 1.683 Wgt., grams 45.4 44.5 44.1 43.7 43.3 43.4 44.5 45.4Comp. (Riehle) .050 .040 .037 .037 .045 .054 .051 .050 {overscore(e)} (C.O.R.) .811 .796 .787 .777 .785 .780 .775 .767 ¹BR-1220 ispolybutadiene manufactured and sold by Shell Chemical Co., Houston,Texas. ²SKI-35 is a polyisoprene available from Muehlstein, H. & Co.,Greenwich, Connecticut. ³ZDA is zinc diacrylate. ⁴6400 P is a powderedpolypropylene available from Amoco Chemical Co., Chicago, Illinois.⁵Trig 17/40 is Trigonex 17/40 manufactured and sold by Akzo ChemieAmerica, Chicago, Illinois. ⁶Papi 94 is a polymeric diisocyanateavailable from Dow Chemical Co., Midland, Michigan.

TABLE 2 Effect of the Addition of Polypropylene Powder Resin as theProperties of the Molded Core Formulations Ingredients 9 10 11 12 13 1415 16 BR-1220 90 90 90 90 90 90 90 90 SKI-35 10 10 10 10 10 10 10 10 ZDA31 31 29 27 25 23 21 20 ZnO 6.0 6.0 6.0 6.0 6.0 6.0 6.0 6.0 ZincStearate 15 15 15 15 15 15 15 15 Limestone 18 18 22 26 32 38 44 50 GrdFlash 20 20 20 20 20 20 20 20 6400 P 0 1 5 10 20 30 40 50 Trig 17/40 1.51.5 1.5 1.5 1.5 1.5 1.5 1.5 Papi 94 .5 .5 .5 .5 .5 .5 .5 .5 Total 192.0193.0 199.0 206.0 220.00 234.0 248.0 263.0 Cost/lb vs. No. 9 — −$.0010−$.0266 −$.0470 −$.0761 −$.1014 −$.1238 −$.1436 Properties Molded CoreSize, inches 1.541 1.540 1.539 1.542 1.542 1.543 1.544 1.544 Wgt., grams36.7 36.6 36.6 37.3 36.7 37.0 36.9 37.0 Comp. (Riehle) .063 .064 .065.057 .064 .062 .064 .063 {overscore (e)} (C.O.R.) .796 .793 .785 .787.759 .744 .720 .705 Molded Ball Size, inches 1.683 1.683 1.683 1.6831.684 1.683 1.684 1.684 Wgt., grams 45.2 45.3 45.3 45.9 45.3 45.4 45.445.4 Comp. (Riehle) .053 .053 .053 .048 .053 .053 .054 .052 {overscore(e)} (C.O.R.) .811 .810 .802 .798 .780 .767 .750 .735 FormulationsIngredients 17 18 19 21 20 BR-1220 90 90 90 90 90 SKI-35 10 10 10 10 10ZDA 20 19 18 17 16 ZnO 6.0 6.0 6.0 6.0 6.0 Zinc Stearate 15 15 15 15 15Limestone 55 60 65 70 75 Grd Flash 20 20 20 20 20 6400 P. 60 70 80 90100 Trig 17/40 1.5 1.5 1.5 1.5 1.5 Papi 94 .5 .5 .5 .5 .5 Total 278.0292.0 306.0 320.0 334.0 Cost/lb vs. No. 9 $.1497 −$.1616 −$.1725 −$.1824−$.1914 No. 9 Properties Molded Care Size, inches 1.542 1.545 1.5451.547 1.546 Wgt., grams 36.9 36.9 36.8 36.8 37.0 Comp. (Riehle) .061.062 .063 .061 .061 {overscore (e)} (C.O.R.) .695 .682 .648 .636 .635Molded Ball Size, inches 1.684 1.683 1.684 1.683 1.682 Wgt., grams 45.445.3 45.3 45.2 45.3 Comp. (Riehle) .053 .052 .053 .053 .053 {overscore(e)} (C.O.R.) .721 .708 .695 .688 .674

As it can be seen in Formulations 1-4, the inclusion of thepolypropylene powder resin (unfluxed) to polybutadiene core compositionshas the effect of producing lighter, harder and slower molded cores. Asa result of the increase hardness, the amount of the zinc diacrylatecrosslinking agent utilized can be reduced in order to soften the moldedcores to a normal compression. See Formulations 5-8.

Moreover, because the specific gravity of polypropylene is very low andthe polypropylene powder resin produces a lighter core when molded,large amounts of higher specific gravity mineral fillers such aslimestone can be added. Consequently, the addition of the polypropylenepowder resin (from 20 to 40 phr in Table 1) allows for a reduction inthe amount of crosslinking agent utilized and an increase in the amountof filler while maintaining the proper weight and compression of themolded cores. In Table 1, Formulation 8 is the preferred embodiment.

Formulations 9-21 set forth in Table 2 further demonstrate the effectproduced by the addition of the polypropylene powder resin (from 1 to100 phr). As the amount of polypropylene is increased, the amount of thezinc diacrylate crosslinking agent is decreased while the amount ofmineral filler (i.e. limestone) is substantially increased (i.e. forexample, in Table 2 an increase in 10 phr of polypropylene powderresulted in a reduction of about 1.5 phr ZDA and an increase of about5.7 phr mineral filler). Due to the decrease in resilience (i.e. C.O.R.)also produced by the addition of the polypropylene powder resin,Formulation 14 is the more preferred embodiment (i.e. optimal hardnessand weight as well as C.O.R.) of the invention.

Furthermore, from a product cost perspective, the addition of thepolypropylene powder (i.e. about $0.36/lb.), and the resulting reductionin the amount of the very expensive crosslinking agent utilized (such aszinc diacrylate), and in turn the increase in the amount of inexpensivemineral fillers (such as limestone at, $0.04/lb.) , the overall cost ofthe molded cores are substantially lowered while the proper weight andcompression is maintained. This is also exhibited in the Formulationsset forth in Table 2.

TABLE 3 Comparison of the Addition of Various Low Specific GravityPowdered Plastics On the Properties of the Molded Cores FormulationsIngredients 22 23 24 25 26 27 28 BR-1220 100 100 100 100 100 100 100 ZDA25 25 25 25 25 25 25 Grd Flash 20 20 20 20 20 20 20 ZnO 5.0 5.0 5.0 5.05.0 5.0 5.0 Zinc 15 15 15 15 15 15 15 Stearate Verflake 25 25 25 25 2525 25 Polyester 0 25 0 0 0 0 0 70 Mesh Nylon 0 0 25 0 0 0 0 70 MeshTexture 5388 0 0 0 25 0 0 0 6800 P 0 0 0 0 25 0 0 7200 P 0 0 0 0 0 25 0Huntsman 0 0 0 0 0 0 25 P.P. 170 231 XL 0.90 0.90 0.90 0.90 0.90 0.900.90 Papi 0.50 0.50 0.50 0.50 0.50 0.50 0.50 Properties Molded CoreWgt., grams 37.0 37.2 36.7 36.0 35.7 35.7 35.8 Comp. 74 58 64 78 55 5455 (Riehle) {overscore (e)} (C.O.R.) .786 .773 .753 .732 .771 .770 .767

The data demonstrates that the addition of the polypropylene powderresin produces enhanced effects (i.e. produces a lighter and hardermolded core) than the remaining powdered thermoplastics tested. While anumber of the powdered plastics did show some enhancement in hardness,the increased hardness was not as significant as that demonstrated bypresent invention and/or the addition of the powdered plastics lead toan increase in weight upon molding and/or a substantial reduction inresiliency was noted. Similar results were also observed through theaddition of powdered polymethyl methacrylate, powdered polyethylene,powdered polystyrene etc. to conventional core compositions.Consequently, the additional powdered plastics failed to exhibit theenhanced effects (i.e. the production of a lighter and harder moldedcore) exhibited by the present invention.

The invention has been described with reference to the preferredembodiments. Obviously, modifications and alterations will occur toothers upon reading and understanding the preceding detaileddescription. It is intended that the invention be construed as includingall such alterations and modifications insofar as they come within thescope of the claims and the equivalents thereof.

Having thus described the preferred embodiment, the invention is nowclaimed to be:
 1. A golf ball having a cover and a core said core beingformed from a composition comprising a base elastomer selected frompolybutadiene and mixtures of polybutadiene with other elastomers, saidpolybutadiene having a molecular weight of from about 50,000 to about500,000, at least one metallic salt of an α, β-ethylenically unsaturatedmonocarboxylic acid, a free radical initiator, and from about 10 toabout 100 parts by weight of a polypropylene powder resin based on 100parts by weight elastomer, wherein said polypropylene powder resinenhances the hardness of the core thereby reducing the amounts of themetallic salt of an α, β-ethylenically unsaturated monocarboxylic acidincorporated with the core relative to cores free of polypropylene. 2.The core as defined in claim 1, wherein said polypropylene powder resinhas a specific gravity of about 0.90 g/cm³ and a melt flow rate of about4 to about
 12. 3. The golf ball as defined in claim 1, wherein said corecomposition comprises from about 20 to about 40 parts by weight of thepolypropylene powder resin based on 100 parts by weight elastomer. 4.The golf ball as defined by claim 1, wherein the composition furthercomprises a modifying ingredient selected from fillers, fatty acids,metal oxides, and mixtures thereof.
 5. The golf ball as defined in claim4, wherein said polypropylene powder resin enhances the hardness of thecore without an increase in weight thereby increasing the amount of amineral filler to be incorporated into the core.
 6. A method ofdecreasing the amount of a metallic salt of an unsaturated carboxylicacid present in a core of a golf ball having a core and a cover, saidcore being formed from a composition having a base elastomer selectedfrom polybutadiene and mixtures of polybutadiene with other elastomers,at least one metallic salt of an α, β-ethylenically unsaturatedmonocarboxylic acid and a free radical initiator, said method comprisingthe step of adding to the core composition from about 10 to about 100parts by weight of a polypropylene powder resin based on 100 parts byweight elastomer, wherein said polypropylene powder resin enhances thehardness of the core thereby reducing the amounts of metallic salt of anα, β-ethylenically unsaturated monocarboxylic acid incorporated withinthe core relative to cores free of polypropylene.
 7. The method of claim6, wherein said polypropylene powder has a specific gravity of about0.90 g/cm³ and a melt flow rate of about 4 to about
 12. 8. A golf ballhaving a core and a cover said core composition comprising an baseelastomer selected from polybutadiene and mixtures of polybutadiene withthe other elastomers, at least one mettallic salt of an α,β-ethylenically unsaturated monocarboxylic acid, a free radicalinitiator, and a filler, wherein the improvement comprises adding fromabout 10 to about 100 parts by weight of a low specific weightpolypropylene powder resin based on 100 parts by weight elastomer toincrease the hardness of the core composition without increasing theweight of the core composition thereby reducing the amount of metallicsalt of an α, β-ethylenically unsatuated monocarboxylic acid andincreasing the amount of filler included in the core compositionrelative to cores free of polypropylene.
 9. The golf ball of claim 8,wherein said polypropylene powder resin has a specific gravity of about0.90 g/cm³, a melt flow rate of about 4 to about 12 and a particle sizedistribution at 20 mesh of about 99 percent.
 10. The golf ball of claim8, wherein said core composition comprises from about 20 to about 40parts by weight of the polypropylene powder resin based on 100 parts byweight elastomer.
 11. A golf ball comprising a cover and an improvedsolid molded core, said solid moled core comprising a base elastomerselected from polybutadiene and mixtures of polybutadiene with otherelastomers, from about 20 to about 50 parts per weight elastomer of atleast one metallic salt of an unsaturated carboxylic acid, from about 1to about 10 parts per weight elastomer of a free radical initiator, andfrom about 0 to about 50 parts per weight elastomer of a filleradditive, wherein the improvement comprises adding from about 10 toabout 100 parts per weight elastomer of a low specific weightpolypropylene powder resin to increase the hardness of the corecomposition thereby decreasing the amount of metallic salt of theunsaturated carboxylic acid included in the core composition relative tothe amount of a metallic salt of an unsaturated carboxylic acid in acore which is free of polypropylene.
 12. The golf ball of claim 11,wherein said polypropylene powder has a specific gravity of about 0.90g/cm³, a melt flow rate of about 4 to about 12 and is in a particle formless than 20 mesh.